Distillation of crude petroleum



Aug 19, l947- w. E. MccoRQUoDALE, JR., Erm. 2,426,110

DISTILLATION OF CRUDE PETRLEUM .Filed oct. 14, 1942 6W/4.0.. wwwa? 4770EA/ YS.

Patented Aug. 19, 1947 nTsTrLLA'rioN or CRUDE PETROLEUM Wilmer E. McCorquodale, .lf-r., rdentown, Del.,

and Lloydv G. Magill, Chesten, Pa., a/ssigno'rsto Sun Gil Company, Philadelphia, Pa., a corporation of New Jersey Application October 14, 1942, Serial No. 462,040 1 claim. (ci. 19e-73)' The present invention relates to a method of distillation and is particularly directed to an improved method of distilling materials such as crude petroleum oils having a relatively wide boiling range in order to produce therefrom desired products.

It is common practice in fractional'distillation of crude petroleum and similar substances to heat the material to be distilled by heat exchange with the hot products from rthe process, after which the lower boiling fractions are separated from the intermediate and higher boiling con'- stituents of the crude by flash distillation. Those constituents of the crude, which are not vaporized by flashing, are then heated by indirect heat exchange in a furnace, the heated products introduced into a vaporization zone, frequently a fractionating tower, and the vapors evolved fractionated into several liquid fractions of Varying boiling points. The vapors of the lowest boiling constituents which are separated by flash distillation after heat exchange with the hot products from the process are frequently introduced into the same fractionating tower as the vapors from the remainder of the crude and all the products are fractionated in the same tower.

This invention is directed to an improvement in a distillation process ofthe type outlined above and in accordance with the present invention the crude oil is first heated by heat exchange with the hot productsfrom the process, the light gasoline vapors are then removed by flashing and the unvaporized, intermediate and higher boiling, constituents are heated in a furnace and introduced into a fractionating tower wherein they are fractionated. The vapors of the`lightgasolinev separated by flashing are condensed and the condensateis introduced into the same fractionating tower employed for fractionating the remainder of the crude. We have discovered that if the light gasoline vapors are condensed and introduced into the fractionating tower as a liquid condensate the same tower is able to handle a substantially greater throughput than is possible when the light gasoline vapors are introduced into the tower in vapor phase. We also discovered that the furnace of a given distillation unit is able to handle a greater throughput if the light gasoline vapors are removed before the remainder of the crude is introduced thereinto. Thus, by a minor and simple modification the throughput of a given distillation unit can be substantially increased.

` For a better understanding of the present invention reference should be made to the accomtower I3.

. 2 panying drawings in which the single gure is a diagrammatic flow chart of apparatus suitable forpracticing the present invention.

Referring now to the drawings I designates a storagetank for crude oil to be distilled. .The crude oil is removed from tank I through line 2 by pump 3 and pumpedy through heat exchangers 4,5 and l'whereinit is heated by indirect heat exchange with the hot products from the process. From heat exchanger 'E the heated `crude oil flows through line 'l having pressure reducing valve 8 therein to flash tower 9 wherein a relatively low pressure, substantially' atmospheric, is maintained. In tower Sthe lowest boiling constituents of the crude oil, light gasoline, vaporize andthe vapors areremoved overhead through line I0 and flow to condenser II wherein they are condensed and the condensate introduced through line I2 into fractionating tower I3. The unvaporized portion of the crude is,V removed from ash tower 9 through line I4and pumped by pump I 5 through the heating coil in furnace IB, the oil being heated during its passage through the furnace to the temperature necessary to provide therequired amounto'f heat for fractionating the crude into 'such portions as are desired. From furnace IS the heated oil flows through line Il having pressure reducingL Valve I8 therein to lower portion of fractionating tower I3, The tower I3 is of conventional design and may be provided with a number of bubble trays therein, the vaporized portion of the heated crude rising upwardly through the. bubble trays in the usual manner and being' fractionated in the usual manner in Froml the top of tower I3 the lightest vapors'of the crude are removed through line' I9 and flow to condenser 2wherein they are cond'ensed, aportion of the kcondensate isr returned through line 2`I to the top of tower I3 to act as reux, while the remainder of the condensate is removed from the process through line 22 and may be pumped to storage or suitable rectification equipment. Several side cuts may be taken in tower I3, and, as illustrated in the drawings, a naphtha side cut may be removed through line 23, the hot naphtha flowing through heat exchanger ll wherein it is cooled by indirect heat exchange with the whole crude oil fiowing therethrough. A gas oil side cut may be removed through line 24, the hot gas oil flowing through heat exchanger 5 wherein it is cooled by heat exchange with the whole crude oil flowing therethrough. From the bottom of tower I3 the residual fuel oil may be removed through line 25 and this product will flow through heat exchanger 3 6 in indirect heat exchange with the whole crude oil flowing therethrough, the fuel oil in line 25 being cooled and the whole crude is further heated.

One of the principal advantages of operating a distillation unit in accordance with the present invention is that with a given throughput rate the vapor velocities in the fractionating tower are substantially reduced over the vapor velocities which would prevail if no flashing operation were employed or if a ashing operation were included but the flashed vapors were added to the fractionating tower in vapor phase. The following specific example will serve to illustrate this and other advantages of the invention.

An East Texas crude oil was withdrawn from storage tank I at a temperature of 74 F. and was pumped through heat exchanger 5 wherein it was heated to a temperature of 189 F. by the indirect heat exchange with hot gas oil which entered the exchanger at 445 F. and was cooled to 145 F. From heat exchanger 5 the crude flowed to heat exchanger 6 wherein it was heated to a temperature of `'280 F. by indirect heat exchange with fuel oil which entered heat exchanger 6 at a temperature of 528 F. and left at a temperature of 270 F. From heat exchanger 6 the heated crude flowed to flash tower 9, the pressure on the crude being reduced to substantially atmospheric pressure on passing pressure reducing valve 8. Substantially ten per cent of the crude was vaporized and the vapors were Withdrawn overhead through line I0 to condenser Il and introduced into fractionating tower I3 through line I2. The temperature of the vapors withdrawn through line Ill and of the reduced crude withdrawn from flash tower 9 through line I4 was 267 F. The reduced crude flowing through line I4 was heated in furnace I6 to 577 F. and the heated reduced crude introduced into fractionating tower I3.

It was found that in the particular distillation unit being studied that, when the charge rate was 840 barrels per hour of whole crude, the maximum vapor velocity in the tower when operating in accordance with the present invention was 836 barrels per hour (expressed as liquid at 60 FJ. In the same distillation unit when operating on the same crude but with the flash tower 9 omitted, the oil flowing directly from line I through line 39 to line I4 by closing valves 8 and 3| and opening valve 32, the maximum vapor velocity in the tower I3 was 1108 barrels per hour. While in the same distillation unit employing the flash tower 9 but omitting the condenser I I and introducing the flashed vapors in Vapor phase into fractionating tower I3 the maximum vapor velocity was 980 barrels per hour. It will thus be seen that the present lnvention permits a substantial decrease in the vapor velocities in the tower or a substantial increase, 20% or more, in the throughput which a given fractionating column can handle and still operate efciently. It should further be noted that the furnace will not need to be redesigned since if the light vapors are ashed from the crude before it is introduced into the heating coil in the furnace, a substantially smaller amount of material flows through the furnace and therefore it can be heated to a higher temperature and thus the throughput of the entire unit is substantially increased.

We claim:

In the process of fractionally distilling crude petroleum in which the crude is preliminarily heated, the pressure thereon then reduced, and by flash distillation the crude is separated into only two products, namely, a vaporized low boiling product which is removed from the ash distillation zone in vapor phase and introduced directly and without previously being subjected to fractionation into a fractional distillation zone and a reduced crude comprising all the constituents of the crude which are not vaporized and which is heated to effect its partial vaporization and then introduced into the same fractional distillation zone at a locus substantially below the locus of introduction of said separated light product, and from which fractional distillation zone its fractional products are separately withdrawn: the herein described improvement which comprises subjecting the separated light vaporous product of flash distillation, while still in vapor phase and prior to any fractionation thereof, to a reduced temperature eective to condense condensible constituents so that said separated light product is introduced into the fractional distillation Zone mainly as a liquid constituent.

WILMER E. MCCORQUODALE, JR. LLOYD G. M'AGILL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,730,891 Leslie et al. Oct. 8, 1929 1,815,127 Dickson July 21, 1931 1,997,675 Bahlke et al. Apr. 16, 1935 2,160,103 Kraft et al. May 30, 1939 2,295,256 Brugma Sept. 8, 1942 1.882,568 Hall Oct. 11, 1932 

